Let's say someone eats a type of cheese that is partially hard cheese & partially non hard cheese. (The mix was intentionally done, incidentally, for explicit purpose of selling it this way. Let's say the cheese is called "Parmerican" - parmesan (aged) + processed "American") Does the person need to wait 6 hours because he ate some hard cheese? How much hard cheese would require waiting 6 hours - does it follow the same concept of "batul beshishim" (less than 1/60) as with milk accidentally mixed into a meat dish (i.e., less than 1/60 is nullified)? Is the amount based on majority (more than 50% hard cheese in the mix means 6 hours) or is there some other measurement in this mix that requires a 6-hour wait?
The concept of bitul b'shishim should certainly apply here. The idea is that any amount less than 1/60th of the volume of the mixture is undetectable (source), and therefore considered to not exist.
Bitul b'rov (nullification by 50%) would not apply in this case as that only works for identical foods. For example, if two non-kosher chicken legs are accidentally mixed up with 3 identical kosher chicken legs, all 5 legs are permitted (do not do this in practice without consulting your rabbi). This would not apply in this case since the hard cheese is clearly not identical to the soft cheese.
Therefore, any cheese mixture that is less than 1/60 hard cheese should not require waiting while any cheese mixture that is more than 1/60 hard cheese would require waiting.